Radio channel allocation for wireless interface using ultra low power nodes

ABSTRACT

An ultra low power wireless node (50) sends (100) a packet on at least two radio channels to a network of backbone nodes (65, 70, 75, 80). Which of the radio channels are listened for at the backbone nodes is allocated (130) according to detected reception performance. The allocating is coordinated for different ones of the backbone nodes. By combining sending on multiple radio channels with dynamically allocating the listening channels according to reception performance and with coordinated allocations for different backbone nodes, the spatial diversity and channel diversity of the separate receiving locations can be exploited. This can make the system more resilient to time varying location specific interference or channel specific interference for example.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a U.S. national phase of International ApplicationNo. PCT/EP2013/064936, filed Jul. 15, 2013, the disclosure of which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to methods of operating a wirelessinterface, to methods of allocating listening radio channels for such aninterface, to corresponding apparatus, to networks having such aninterface, and to corresponding computer programs.

BACKGROUND

Wireless networks based on a standard like IEEE 802.15.4 (/ZigBee), IEEE802.11 (/Wi-Fi) or IEEE 802.15.1 (/Bluetooth) are commonly known. Theseoperate in the 2400-2483.5 MHz ISM band (Industrial, Scientific andMedical) band. They are relatively low power short range systems (10-100m) and can be interfered by other radios that are nearby and can causehigh interference levels on nearby frequencies. This can be a constrainton attempts to reduce power consumption in wireless interfaces.

ZigBee for example is a low data rate (250 kbit/s) system with securityfeatures and enables a mesh network to be created ad hoc, to enable anydevice to reach more distant devices. In 2012 the ZigBee PRO Green Powerfeature was announced which allows ultra low power devices such asbattery-less devices to securely join ZigBee PRO networks through awireless interface which is designed to minimise the amount of powerused. It is a more eco-friendly way to power ZigBee products such assensors, switches, dimmers and many other devices. These devices can nowbe powered just by harvesting widely available, but often unused sourcesof small amounts of energy such as motion, light, vibration.

Devices can use energy harvesting to overcome the disadvantages of beingmains powered or battery powered. Mains powering a device results in aninstallation cost, and it can only be used for non-mobile devices. Thebatteries of battery powered devices have a limited lifetime and theeconomic and environmental cost of regularly replacing batteries is notalways acceptable.

Ultra Low Power (ULP) wireless nodes are characterized by the fact thatthey require zero-maintenance (no battery replacements), without theneed to be mains powered. This can be achieved in principle in severalways. A first possibility is by making the battery lifetime larger thanan expected or designed product lifetime by reducing the powerconsumption, such that the batteries last longer than the expectedlifetime of the product. In this case the product lifetime has an upperbound set by the self-depletion of the battery.

A second possibility either instead of or together with firstpossibility is to use energy harvesting techniques. By reducing thepower consumption, such that the required power/energy levels can beharvested from the environment. Energy harvesting is commonly regardedas deriving energy from external sources (e.g., solar power, thermalenergy, wind energy, salinity gradients, and kinetic energy), and usingor storing it for small, wireless autonomous devices, like those used inwearable electronics and wireless sensor networks. ZigBee Green Power[2] is an extension to the ZigBee PRO networking stack [1] that allowsincorporating ultra low power nodes—with a focus on energy harvestednodes—in a ZigBee PRO network. ZigBee Green Power enables ultra lowpower devices to use a wireless interface to complete a communication toa backbone network using typically hundreds of microJoules of energy.There are three type of nodes involved:

GreenPower Device

The GreenPower Devices (GPD) are a type of ultra low power wirelessnodes. They typically generate the commands that should have an effecton the sink nodes (GPS) in the backbone network such as a ZigBee PROnetwork. One example is an energy harvesting switch (being a GPD) thatgenerates a Toggle command, to toggle the state of a lamp (being a GPS)on the ZigBee PRO network. Because of these restrictions in energy, GPDscan only transmit the packets a limited number of times: typically theybroadcast packets 3 times on a single channel. This channel ispredefined, is configured using switches on the device itself, or can benegotiated during an initial commissioning procedure. In its simplestform the GPD can only transmit packets, and cannot receive any packet.

GreenPower Proxy

The GreenPower Proxies (GPP) are the nodes on the backbone network(ZigBee PRO network for example) that are mains powered and, when theyare within radio range of the GPD, pick up the packets broadcast by theGPD, and deliver them to the sink nodes (GPS) over the ZigBee PRObackbone network. Since the GPD broadcasts its messages, these can bereceived by multiple GPPs, creating a form of redundancy in the network.The GPPs can fulfill an application level role at the same time.

Mains Powered GreenPower Sink

The GreenPower Sinks (GPS) are the nodes on the ZigBee PRO network thatare mains powered and can have an application level entity which can becontrolled by the GPD. For example, a lamp that is toggled by the energyharvesting switch at the GPD. The GPS does not need to be in radio rangeof the GPD, but has to be connected over the ZigBee PRO network with oneor more proxy nodes (GPP) within radio range of the GPD. GPS nodes canoften also act as GPP nodes directly.

SUMMARY OF THE INVENTION

An object is to provide improved methods, devices, networks andprograms. An aspect of the invention provides a method of operating awireless interface for communicating between an ultra low power wirelessnode and a network of backbone nodes, by making transmissions from theultra low power wireless node to send the same packet on at least tworadio channels, receiving the transmissions carrying the packet at thebackbone nodes, and detecting reception performance of the wirelessinterface. There is also a step of dynamically allocating which of theradio channels are listened for at the backbone nodes according to anindication of the detected reception performance, wherein the allocatingcomprises making coordinated allocations for different ones of thebackbone nodes.

By combining sending on multiple radio channels with dynamicallyallocating the listening channels according to reception performance andwith coordinated allocations for different backbone nodes, the spatialdiversity and channel diversity of the separate receiving locations canbe exploited. This can make the system more resilient to time varyinglocation specific interference or channel specific interference forexample. This means the probability of reception outage can be reducedcompared to channel allocations made independently for each backbonenode without coordination. This is particularly useful where there islittle or no adaptability in the transmitting side. The benefits canapply for various different types of coordination, for example whetherthe detections are collected from different backbone nodes and theallocations are determined together from the collected information, orwhether candidate allocations are made separately from local detections.In the latter case the coordinating can involve comparing the candidateallocations and adjusting them to form a desired pattern of allocations.See FIGS. 3, 4 and 5 for example.

Embodiments can have additional features added, or such features can bedisclaimed to define claims, and some of such additional features aredescribed in more detail and set out in dependent claims. One suchadditional feature is the step of making the transmissions from theultra low powered wireless node being made without dynamic radio channelselection based on radio channel selection feedback information from thebackbone nodes. By avoiding dynamic selection of radio channel, the ULPnode can avoid consequences such as added power consumption, add costsand add complexity at the ultra low power wireless node. See FIGS. 3 and6 for example.

Another aspect provides a method of allocating listening radio channelsfor a wireless interface for communicating between an ultra low powerwireless node and a network of backbone nodes, for use when the ultralow power wireless nodes send transmissions having the same packet on atleast two radio channels, for receiving at the backbone node, having thesteps of receiving an indication of reception performance of thewireless interface, and allocating dynamically which of the radiochannels are listened for at the backbone nodes according to theindication of reception performance, wherein the allocating comprisesmaking coordinated allocations for different ones of the backbone nodes,and outputting the allocations to the backbone nodes. This correspondsto the first aspect but encompasses the allocating part for the firstaspect. See FIGS. 4, 7 and 9 for example.

An additional feature is the indication of reception performance of thewireless interface comprising at least one of: an indication ofreception performance of the transmissions detected by the backbonenodes, and an indication of wireless interference detected otherwise.This can enable further refinement of allocations to suit differentconditions and different types of interference. See FIG. 6, 8 or 10 forexample.

Another such additional feature is the indication of receptionperformance of the transmissions comprising at least one of: anindication of whether the packet was received by the backbone nodes, anRSSI associated with the packets received by the backbone nodes, and anyother link quality indication of the packets received by the backbonenodes, and wherein the indication of wireless interference detectedotherwise comprises at least one of: an RSSI level of the interferencemeasured, the carrier sense assessments of interference measured,correlation of the interference over multiple channels, correlation ofinterference over multiple backbone nodes and interference detected atthe ultra low power wireless node and sent to the backbone nodes. Theseare accessible, relatively convenient to measure, and commonly supportedby available hardware, though others can be envisaged. See FIGS. 6, and8 for example.

Another such additional feature is the step of allocating comprisingpassing the detections of reception performance by at least two of thebackbone nodes to a common location and making the allocations based onthe detections collected at that common location. By collecting thedetections, a desired pattern of allocations can be made convenientlyfrom the same basis. This may be more efficient than alternatives suchas making candidate allocations from local detections then coordinatingby collecting and adjusting the candidate allocations rather thansharing the detections. See FIGS. 8 to 11 for example.

Another such additional feature is determining outage probabilities foreach radio channel for each of the backbone nodes for different patternsof listening channel allocations according to the detections andcarrying out the allocating based on the determined outageprobabilities. This is a convenient way to enable different patterns ofallocations to be assessed. See FIGS. 9 to 11 for example.

Another such additional feature is the allocating being biased to bemore dependent on more recent ones of the indications of receptionperformance. This can help make the adapting more responsive to rapidchanges in reception conditions. See FIG. 10 for example.

Another such additional feature is the transmissions comprisingtransmissions from at least two ULP wireless nodes, and the allocatingstep comprises making allocations for listening channels of the backbonenodes from the set of transmit channelsused by the at least two ULPwireless nodes. This can provide more reception performance informationand lead to better coordinated allocation. See FIG. 11 for example.

Another such additional feature is the step of determining outageprobabilities for each of the ULP wireless nodes for each of thebackbone nodes for each of the radio channels for each of the channelallocation patterns. This can help enable the allocation to be optimisedfor multiple ULP wireless nodes which may have different outageprobabilities even for the same radio channels. See FIG. 11 for example.

Another such additional feature is the step of making the allocations isalso dependent on locations of the ULP wireless nodes and the backbonenodes where detections of reception performance are made. This canfurther improve the allocations by enabling better correlation ofdetections to determine whether detected interference is locationspecific for example, or to interpolate between detections at differentlocations. See FIG. 12 for example.

Another aspect provides apparatus for allocating listening radiochannels of a wireless interface for communicating between an ultra lowpower wireless node and a network of backbone nodes, for use when theultra low power wireless nodes are arranged to send transmissions havingthe same packet on at least two radio channels, for receiving at thebackbone nodes, the apparatus having an input for receiving anindication of reception performance of the wireless interface. There isalso a processor configured to allocate dynamically which of the radiochannels are listened for at the backbone nodes according to thedetections of reception performance, wherein the allocating comprisesmaking coordinated allocations for different ones of the backbone nodes,and outputting the allocations to the backbone nodes. This correspondsto the above allocating methods. See FIGS. 3 and 7 for example.

An additional feature is the processor also being configured todetermine outage probabilities for each radio channel for each of thebackbone nodes for different patterns of listening channel allocationsaccording to the indications and to carry out the allocating based onthe determined outage probabilities. See FIGS. 7 to 12 for example.

Another aspect provides a network having the apparatus set out above andhaving backbone nodes coupled to the apparatus, the backbone nodes beingconfigured to detect the reception performance and to send theindications of the reception performance to the apparatus. See FIG. 3for example.

Another aspect provides a computer program for allocating listeningradio channels for a wireless interface for communicating between anultra low power wireless node and backbone nodes, for use when the ultralow power wireless nodes send transmissions having the same packet on atleast two radio channels, for receiving at the backbone nodes, theprogram having instructions for causing a processor to carry out themethod set out above. See FIG. 7 for example.

Any of the additional features can be combined together and combinedwith any of the aspects. Other advantages will be apparent to thoseskilled in the art, especially over other prior art. Numerous variationsand modifications can be made without departing from the claims of thepresent invention. Therefore, it should be clearly understood that theform of the present invention is illustrative only and is not intendedto limit the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

How the present invention may be put into effect will now be describedby way of example with reference to the appended drawings, in which:

FIGS. 1 and 2 show schematic views of networks according to conventionalprior art techniques,

FIG. 3 shows a schematic view of a network according to an embodiment,

FIG. 4 shows steps of a method of operating according to an embodiment,

FIG. 5 shows a time chart of a sequence of steps according to anembodiment,

FIG. 6 shows a time chart of a sequence of steps according to anembodiment,

FIG. 7 shows a schematic view of an allocation processor according to anembodiment,

FIG. 8 shows steps of a method of operating according to an embodimentshowing various ways of detecting reception performance,

FIG. 9 shows steps of a method of allocating listening channelsaccording to an embodiment using an outage probability matrix,

FIG. 10 shows another embodiment with allocation biased towards morerecent reception performance,

FIG. 11 shows another embodiment showing reception performance detectionand allocation coordinated for multiple ULP nodes, and

FIG. 12 shows another embodiment showing allocation based on correlationbased on locations of detections.

DETAILED DESCRIPTION

The present invention will be described with respect to particularembodiments and with reference to certain drawings but the invention isnot limited thereto but only by the claims. The drawings described areonly schematic and are non-limiting. Where the term “comprising” is usedin the present description and claims, it does not exclude otherelements or steps. Where an indefinite or definite article is used whenreferring to a singular noun e.g. “a” or “an”, “the”, this includes aplural of that noun unless something else is specifically stated.

Elements or parts of the described nodes or processors may compriselogic encoded in media for performing any kind of informationprocessing. Logic may comprise software encoded in a disk or othercomputer-readable medium and/or instructions encoded in an applicationspecific integrated circuit (ASIC), field programmable gate array(FPGA), or other processor or hardware.

References to programs or software can encompass any type of programs inany language executable directly or indirectly by a processor.

References to logic, hardware, processor or circuitry can encompass anykind of logic or analog circuitry, integrated to any degree, and notlimited to general purpose processors, digital signal processors, ASICs,FPGAs, discrete components or transistor logic gates and so on.

References to ultra low power nodes are intended to encompass wirelessnodes having protocols designed for a lower power consumption by theirwireless parts than the power used by the backbone nodes they are tocommunicate with. In particular examples the lower power consumption canbe lower than a conventional ZigBee node. In more particular examplesthe nodes are designed to be self powering without maintenance for theirdesign lifetime. In particular they may have an energy harvesting powersource and/or a battery power source, designed so that they never need areplacement battery. In particular examples the power consumption can beless than 10 milliJoules per packet transmission, or less than 1milliJoule per packet transmission.

References to backbone nodes are intended to encompass nodes of any kindof network, not limited to the ZigBee nodes of the examples described.

ABBREVIATIONS

-   BER bit error rate-   BBN(s) Backbone node(s)-   GPD Green Power Device-   GPP Green Power Proxy node-   GPS Green Power Sink node-   LQI link quality indicator-   PER packet error rate-   RSSI received signal strength Indicator-   SIR signal-to-interference ratio-   SNR signal-to-noise ratio-   TX Transmitter-   ULP Ultra Low Power-   ULPNs Ultra Low Power node(s)

REFERENCED DOCUMENTS

-   [1] ZigBee Specification, ZigBee Alliance, Revision 20, Sep. 19,    2012-   [2] ZigBee Green Power Specification, ZigBee Alliance, Revision 23,    Version 1.0, Aug. 22, 2012-   [3] Multi-Channel Wireless Sensor Networks: Protocols, Design and    Evaluation, Ozlem Durmaz Incel, University of Twente, The    Netherlands

IEEE 802.15.4 is the basis for networking stacks like ZigBee RF4CE,ZigBee PRO and ZigBee IP, as well as other standards and proprietarystacks.

FIGS. 1, 2, Introduction to Some Issues with Conventional WirelessInterfaces for ULP Nodes.

FIG. 1 shows a typical scenario according to conventional practice. Areliable backbone network is provided such as a ZigBee PRO network usingacknowledged transmissions and extensive number of retries, both on ahop-by-hop and end-to-end level. This has a number of Green Power proxynodes A, B, C, D 15, 20, 25, and 35 and a Green Power sink backbone node30. These are coupled by reliable wireless links. A Green Power deviceGDP (or ULP) node 10 tries to communicate with the sink node 30 via anunreliable ultra low power wireless interface, having no acknowledgementand no adaptive transmission channel selection.

The GPD broadcasts the packet multiple times on the same radio channel.There are three GPPs (A, B, C) within the radio range of the GPD. Two ofthe GPPs (A, B) pick up the packet at least once. The third GPP (C)fails to receive any of the broadcasted packets (since it is located ina fading dip). The first two GPPs will deliver the packet to the desireddestination (sink node) over the reliable backbone network formed by theZigBee PRO network. In this case, the second packet transmission isredundant, since even when only one of A or B had received the packetand delivered it to C, the system would have operated correctly.

As described in [1], when a ZigBee PRO coordinator starts a new network,it will scan all channels to find out what channels are already in useby other (ZigBee PRO) networks in the neighborhood and it will avoidsetting up its own network on one of these channels. As described in[3], when the bandwidth offered by a single channel is not sufficient,the network can use multiple channels to increase the availablebandwidth and associated throughput. The GreenPower Devices always sendtheir packets on a single channel.

FIG. 2 shows a similar schematic view of the same network, but in thesituation that the reception conditions for the unreliable ultra lowpower wireless network are worse. As shown in FIG. 2, the single radiochannel is compromised, and none of the packets is received by any ofthe backbone nodes, and the communication fails. Hence if this channelis compromised due to interference, the reliability of the communicationcan be hampered. Since the transmissions are broadcasted and as suchunacknowledged, the GreenPower Devices do not notice the interference,and cannot take counter measures such as retransmitting, delaying, orchanging the transmission channel.

Introduction to Some Features of Embodiments:

Instead of transmitting the same packet a number of times on a singlechannel, in embodiments described below, the GreenPower Device (ULPnode) transmits the same packet on a number of different channels. Thiscan extend the redundancy in the network to the channel domain. Thisredundancy can be exploited by having the listening channels of theGreenPower proxies (receiving Backbone nodes) spatially distributed in auniform way, to optimize the chance of receiving the packet of theGreenPower device (ULP node) in case a channel gets compromised due tointerference.

By allocating the listening channels of the backbone nodes dynamicallyaccording to reception performance, rather than according to a staticpredetermined pattern, the wireless interface can be made more resilientto actual conditions.

In the following description, Ultra Low Power nodes, which are not onthe backbone network, are called ULP nodes and may be referenced bycapital letters, e.g. Node A, Node B.

Nodes on the backbone network are called Backbone nodes and may bereferenced by numbers, e.g. Backbone Node 1, Backbone Node 2.

Packets are referenced by Greek letters, derived from the ULP node bywhich they are transmitted, and have a subscript indicating the order oftransmission of the packet:

-   -   a_(i) is the i-th packet transmitted by ULP Node A    -   β_(k) is the k-th packet transmitted by ULP Node B        FIG. 3, Network View According to an Embodiment

FIG. 3 shows a schematic view of a network according to an embodiment.In this case the backbone network is shown with three receiving nodes65, 70 and 75 within range of a ULP node 50. Backbone node 80 is a sinkfor the communication from the ULP node. The ULP node has at least aradio transmitter capable of transmitting on at least two radiochannels. The set of Backbone nodes are connected with each other over awireless or wired backbone network, and at least some of these Backbonenodes are equipped with at least a radio receiver capable of receivingpackets on the same radio channels used by the ULP node fortransmitting. A listening channel allocation processor 90 is providedfor allocating listening channels to the different backbone nodes whichcan receive from the ULP node via the ultra low power wireless network.

The ULP node broadcasts its packets on at least two radio channels, so apacket a_(i) broadcasted by ULP Node A, is received by a subset of theBackbone nodes. For each of the Backbone nodes and for each of the radiochannels ULP Node A is capable of transmitting on, the allocationprocessor dynamically (regularly or triggered by the reception by thebackbone network of a packet transmitted by the ULP node) determineschannel allocations by estimating the reception performance of the ultralow power wireless interface. This can be based on for example packeterror rates for a future packet a_(i+n) with n>0, based on for examplethe information of whether the packet a_(i) was or was not received bythe respective Backbone nodes, and the channel, signal strength and linkquality associated with the eventual reception.

Combining the estimated packet error rates on a network scale level, theallocation processor can dynamically allocate the listening channel ofthe Backbone nodes, in order to maximize the probability that a futurepacket a_(i+n) is received by at least one of the Backbone nodes, incase of interference on one or more of the radio channels ULP Node A isbroadcasting. The allocation processor can be located anywhere and canbe centralized or distributed. One option is to have it co located orintegrated with the sink node, or incorporated as a function of any nodewhen it acts as a sink node. This is convenient as the sink nodereceives the packets from the receiving backbone nodes and thus caneasily receive detections of reception performance from these receivingbackbone nodes.

Notably this allocation feature contrasts with a conventional ZigBeeGreen Power node which transmits on only one predetermined channel, solistening channels are pre determined and there was no adaptation of thelistening channels, so no need for a dynamically adaptable listeningpattern. It also contrasts with a cellular network which can receive atmultiple base stations but does not allocate listening channels becausebase stations listen on all channels and feedback info to a mobiledevice for it to select a radio channel to transmit on, so again thereis no dynamically adaptable pattern of listening channels coordinatedfor different backbone nodes.

In some examples the ULP node has no wireless receiver capability, inothers it has a limited very low power receiver which is only usedsparingly, such as for commissioning, not during typical communicationsoperations.

FIGS. 4, 5 6 Flow Chart and Time Charts According to Embodiments

FIG. 4 shows steps carried out in operating the ultra low power wirelessinterface according to an embodiment. At step 100, the ULP nodebroadcasts its packets on at least two radio channels. At step 110,nodes of the backbone receive packet a_(i) broadcasted by ULP node. Atstep 120, for each of the backbone nodes and for each of the radiochannels used by the ULP node, reception performance of the ultra lowpower wireless interface is detected. Which of the radio channels arelistened for at each backbone node is allocated at step 130 according tothe detections of reception performance and the listening channelallocations are coordinated for different ones of the backbone nodes.

FIG. 5 shows a time chart for corresponding steps, with time flowingdown the figure. A left hand column shows actions at the ULP node. Anext column shows actions at a receiving backbone node. A next columnshows actions at a backbone node acting as a sink, and the right handcolumn shows actions of the listening channel allocation processor. Asin FIG. 4, the ULP node broadcasts the same packet using a set of two ormore radio channels. Backbone nodes acting as receivers receive thepacket and pass it on towards the sink node. The sink backbone nodereceives the packet and has application level software and hardware forusing the packet. The backbone nodes may also detect receptionperformance and pass this on to the listening channel allocationprocessor. This allocation processor allocates the channel to belistened to by backbone nodes according to the detected receptionperformance and coordinates the allocations for different backbonenodes.

In some embodiments the allocation can use the information from multiplepackets transmitted by the same ULP node. A series of packets a_(i),a_(i+1), . . . , a_(i+k) broadcast by ULP Node A are received by asubset of the Backbone nodes. For each of the Backbone nodes and foreach of the radio channels ULP Node A is capable of transmitting on,dynamically (regularly or triggered by the reception by the backbonenetwork of a packet transmitted by the ULP node) the allocationprocessor estimates the packet error rates for a future packet a_(i+n)with n>k, based on whether each of the packets in the series of packetsa_(i), a_(i+1), . . . , a_(i+k) was or was not received by therespective Backbone nodes, and the channel, signal strength and linkquality associated with the eventual receptions.

Combining the estimated packet error rates on a network scale level, theallocation processor can dynamically allocate the listening channels ofthe Backbone nodes, in order to maximize the probability that a futurepacket a_(i+n) is received by at least one of the Backbone nodes, incase of interference on one or more of the radio channels ULP Node A isbroadcasting.

FIG. 6 shows a similar time chart to that of FIG. 5. In this case, theULP node broadcasts without dynamic channel selection based on anyfeedback of interference levels. The reception performance detectionscan include detecting RSSI associated with the packet, and RSSIassociated with other packets on the same or other radio channels, anRSSI level of interference measured, and carrier sense assessments ofinterference measured. The allocation processor can also determine anduse correlations of the interference over multiple channels, andcorrelations of interference over multiple backbone nodes. In some casesaccurate timing information of the interference detected at thedifferent locations can be compared to enable correlation of theinterference detections in time over multiple backbone nodes. This canbe used as another factor when making the coordinated allocations of thechannels of the different backbone nodes.

FIG. 7, Listening Channel Allocation Processor

FIG. 7 shows a schematic view of an example of a listening channelallocation processor 90. It has a program 94 for making allocationsaccording to detected reception performance information received frombackbone nodes or elsewhere, and for coordinating allocations fordifferent backbone nodes. This program passes outputs to a program 96for sending out allocations to respective backbone nodes. The programscan be executed by any kind of general purpose processor or morespecific circuitry following established practice, and can be divided upinto modules as desired.

FIG. 8 Method Showing Various Reception Performance Measures

FIG. 8 shows steps of a method of operating according to an embodimentsimilar to that of FIG. 4 and showing various ways of detectingreception performance. As in FIG. 4, at step 100, the ULP nodebroadcasts its packets on at least two radio channels. At step 110,nodes of the backbone receive packet a_(i) broadcasted by ULP node. Atstep 120, for each of the backbone nodes and for each of the radiochannels used by the ULP node, reception performance of the ultra lowpower wireless interface is detected. Which of the radio channels arelistened for at each Backbone node is allocated at step 130 according tothe detections of reception performance and the listening channelallocations are coordinated for different ones of the Backbone nodes.Step 120 has two parallel sub steps as shown, any or all of which may beused. At step 300, RSSI associated with the packet is detected at eachBackbone node which receives the packet, and is passed on to the sinkbackbone node. At step 310, indications of wireless interference aredetected such as RSSI of the interference measured at the same or otherradio channels at the Backbone node, carrier sense assessments of theinterference measured at the same or other radio channels at theBackbone node, and interference detected at the ULP node for example.This can also include the correlation of the interference over multiplechannels, and accurate timing information of the interference allowingthe correlation of the interference over multiple backbone nodes to beassessed later on.

Reception Performance

In a radio device the received signal strength indicator (RSSI) circuitprovides measurement of the power present in a received radio signal.The RSSI is the relative received signal strength in a wirelessenvironment, in arbitrary units for power level and within a certainrange (range of RSSI values). The RSSI can be measured during (preamble)packet reception and/or without packet reception. The measurementrelates normally to the received radio signal including various stagesof filtering, thus to some in-channel power level.

Carrier sense methods in wireless networking can be based on receiverprocessing to verify if a (preamble of a) packet is present and/oranother signal is present, and optionally if the received signalstrength is above a certain threshold level.

Link quality relates to the relative signal strength, signal-to-noiseratio, signal-to-interference ratio, signal distortion (as result ofchannel response degradation including multipath effects) and/or acombination of these.

FIG. 9, Allocation Method Using Outage Probability Matrix

FIG. 9 shows steps of a method of allocating listening channelsaccording to an embodiment using an outage probability matrix. Step 200shows collecting indications of reception performance such as RSSI fromdifferent BBNs. This is used to update a database of receptionperformance information for different BBNs and different channels atstep 210. Then an outage probability matrix for various possibleallocation patterns for different BBNs and different radio channels canbe derived from the reception performance database at step 220. Anallocation pattern of listening channels can then be selected accordingto their corresponding outage probabilities at step 230, and theselected allocation information can be sent to backbone nodes at step240. An example of the outage probability matrix will be described inmore detail below.

Outage Probability

A packet error rate (PER) and/or bit error rate (BER) of a data receiverdepends on the receive conditions as receive level of the desiredsignal, interference and/or noise level, signal-to-interference ratio(SIR) and/or signal-to-noise ratio (SNR). In one example a link isregarded as unreliable when the packet error rate (PER) is higher than5%. This will occur with a certain transceiver system (modulation type,spreading, coding, low receiver noise) with a SIR lower than 5 dB. Witha SIR lower (worse) than 5 dB, the PER will be higher (worse) than 5%.

In one example the link is regarded as having an outage (outageprobability of 100%) when the PER is permanently worse than 5%. Theoutage probability corresponds to the probability the PER exceeds 5% (orthe SIR drops below 5 dB).

BBN Receive Level

A BBN (Backbone node) is normally operating in the receive mode on asingle channel to anticipate on a transmission by a ULPN, but at regularintervals it switches to listen for one or more other channelfrequencies to measure the RSSI (receive signal strength indicator)level to characterize the (in-channel) interference level.

A BBN receives transmissions of a single ULPN at approximately the samereceive level and in case the BBN switches to listen to another channel,about the same receive level can be expected. (Note there is a certainfrequency selective variation, but in this example this is assumed to benegligible.) The RSSI measured with such transmissions by a single ULPNgives some variation (over time and over channel frequencies). Somevariation occurs due to fading/shadowing for example by a person walkingthrough a room and standing near the ULPN light switch, but suchvariation is assumed here to be negligible.

The outage probability with regard to a certain BBN and a certain ULPNon a certain channel frequency corresponds to probability ofinterference at the BBN, and corresponds to the probability that theinterference is larger than the receive level for the ULPN minus 5 dB inthis example. Such an outage probability for the certain BBN, certainULPN and certain channel can be estimated by measurements of the RSSIlevel by the BBN during the reception of the ULPN transmission comparedto measurements of interference level taken at moments when there is noULPN transmission. Next, the outage probabilities for all ULPNs, allBBNs and all channels can be estimated likewise. Then, at some centralprocessing point all outage information can be combined to determine thepreferred setting of the BBN channel frequencies.

Example with 2 ULPNs

An example with 6 BBNs (m=0, 1, . . . 5), 2 ULPNs (n=0, 1), and 3channel frequencies (k=0, 1, 2) will be described. First the steps ofdescribing the receive levels at the 6 BBNs with regard to the 2 ULPNsare taken. The matrix below characterizes the RSSI with regard to indexm,n with m referring to the BBN and n to the ULPN. When a BBN cannotreceive a certain ULPN some lower RSSI reference level is used for therssi_(m,n) in question.

TABLE 1 matrix of receive performance information RSSI_BBN-ULPNrssi_(0, 0) rssi_(0, 1) rssi_(1, 0) rssi_(1, 1) rssi_(2, 0) rssi_(2, 1)rssi_(3, 0) rssi_(3, 1) rssi_(4, 0) rssi_(4, 1) rssi_(5, 0) rssi_(5, 1)

The interference level distribution can be measured at each BBN bymeasuring the RSSI at regular intervals when there is no ULPNtransmission detected. Such interference RSSI measurement information ata certain BBN and a certain channel can be combined with the abovementioned RSSI_BBN-ULPN matrix to derive the outage probability withregard to m/n/k-th BBN/ULPN/channel.

The matrix below reflects the probability of a SIR level related to them/n/k-th BBN/ULPN/channel that is lower than 5 dB. The first 3 columns(with middle index 0) refer to links from ULPN₀ and the last threecolumns (with middle index 1) refer to ULPN₁. (with C ULPNs this matrixwill grow to C×3 columns).

TABLE 2 outage probability matrix Outage_BBN-ULPN-channel out_(0, 0, 0)out_(0, 0, 1) out_(0, 0, 2) out_(0, 1, 0) out_(0, 1, 1) out_(0, 1, 2)out_(1, 0, 0) out_(1, 0, 1) out_(1, 0, 2) out_(1, 1, 0) out_(1, 1, 1)out_(1, 1, 2) out_(2, 0, 0) out_(2, 0, 1) out_(2, 0, 2) out_(2, 1, 0)out_(2, 1, 1) out_(2, 1, 2) out_(3, 0, 0) out_(3, 0, 1) out_(3, 0, 2)out_(3, 1, 0) out_(3, 1, 1) out_(3, 1, 2) out_(4, 0, 0) out_(4, 0, 1)out_(4, 0, 2) out_(4, 1, 0) out_(4, 1, 1) out_(4, 1, 2) out_(5, 0, 0)out_(5, 0, 1) out_(5, 0, 2) out_(5, 1, 0) out_(5, 1, 1) out_(5, 1, 2)

Each BBN operates to listen on one channel (apart from time to timeduring a short interval measuring the interference RSSI), which meansthat within both the first 3 elements of each row (and the last 3elements of each row) only one outage element is relevant. Such relevantoutage element for the m-th row corresponds to the channel at which then-the BBN is operating.

Consider a channel combination with the 0-, 1-, . . . 5-th BBN operatingrespectively at the 1-, 2-, 0-, 0-, 2-, 2-th channel. Then severalmatrix elements Outage_BBN-ULPN-channel have to be filled in with thevalue 1. Such a 1 means an outage of 100% because that channel is notused by the corresponding BBN and from the corresponding BBN and channelthere is no contribution to the overall successful transfer to the sink.The filling with 1's is identical between the left and right (3 column)part since the channel in use at a certain BBN is the same for the twoULPNs.

TABLE 3 matrix Outage_BBN-ULPN-combination 1 out_(0, 0, 1) 1 1out_(0, 1, 1) 1 1 1 out_(1, 0, 2) 1 1 out_(1, 1, 2) out_(2, 0, 0) 1 1out_(2, 1, 0) 1 1 out_(3, 0, 0) 1 1 out_(3, 1, 0) 1 1 1 1 out_(4, 0, 2)1 1 out_(4, 1, 2) 1 1 out_(5, 0, 2) 1 1 out_(5, 1, 2)

There are 3⁶ channel combinations possible with the 6 BBNs and the aimis to select the best of these channel combinations. In this examplesome correlation is assumed between presence of interference at thedifferent BBNs that operate at the same channel. For this reason it isassumed that the risk on not receiving correctly the packet from an ULPNby one of these BBNs operating at the same channel is much higher thanthe multiplication of the risks by the BBNs on the channel in question.Therefore in this example an approximation for the outage metric isbased on only the outage of the BBN operating at a certain channel thathas the best (that is minimum) outage with respect to a certain ULPN:Outage_BBNs−0-th ULPN−0-th channel=Min(out_(2,0,0),out_(3,0,0))Outage_BBNs−0-th ULPN−1-th channel=Min(out_(0,0,1))Outage_BBNs−0-th ULPN−2-thchannel=Min(out_(1,0,2),out_(4,0,2),out_(5,0,2))

In this example it is assumed that there is no correlation between thepresence of interference on the different channels. (This occurs whenthe bandwidth of interference is small compared to spacing of thechannel frequencies like with Bluetooth, microwave oven etc. Thisassumption does not hold in situations when the bandwidth of theinterference is not small compared to the spacing of the channelfrequencies, like with Wi-Fi with 11 n channel bounding)

In this example with 6 BBNs, 2 ULPNs and 3 channel frequencies it isassumed that the outage probability with regard to 0-th and 1-th ULPNcan derived with using multiplication of intermediate results perchannel, and calculation becomes as follows:Outage_BBNs−0-th ULPN−allchannels==Min(out_(2,0,0),out_(3,0,0))*Min(out_(0,0,1))*Min(out_(1,0,2),out_(4,0,2),out_(5,0,2))andOutage_BBNs−1-th ULPN−allchannels==Min(out_(2,1,0),out_(3,1,0))*Min(out_(0,1,1))*Min(out_(1,1,2),out_(4,0,2),out_(5,1,2))

For practical reasons the best overall system outage is taken as thesituation where the worst (largest) of the outages for the 0-th and 1-thULPN has to be optimized (minimized). This can be represented as findingthe situation with the minimum of the following:Max[Min(out_(2,0,0),out_(3,0,0))*Min(out_(0,0,1))*Min(out_(1,0,2),out_(4,0,2),out_(5,0,2)),Min(out_(2,1,0),out_(3,1,0))*Min(out_(0,1,1))*Min(out_(1,1,2),out_(4,0,2),out_(5,1,2))]

Thus with all of the 3⁶ channel combinations the abovementionedMax . . . [Min*Min*Min,Min*Min*Min]can be calculated.

Next the best channel combination can be found with lowest Max (lowestoutage).

An initial channel combination to start with, can be based on randomchannel assignment or fixed sequence assignment.

Adaptation of the channel settings can be made all at once or with stepby step changes and excluding combinations occurring in between thatprovide a bad overall outage. Other intermediate approximations tocalculate some outage metrics that are different from the ones followedin this example, can be followed. The above described optimization isbased on a number assumptions with respect to a simplified outage modeland certain interference correlation condition (related to time ofoccurring, between channels, between BBN positions). In practice thereare always Gaussian-like variations and simplified first orderapproximation modelling and optimization can give a major performanceimprovement. More refined modelling with say 5-step histogramdistribution information processing can improve this further but wouldrequire more dedicated processing.

In some cases information on the current interference level of thedifferent channels (like energy density and carrier sense) can bemeasured by the ULPN and transferred to the backbone network byincluding this information in the packets transmitted by the ULPN, whenestimating the packet error rate for future packets on the differentchannels.

In some examples a history of the reception performance in terms of RSSIor other interference level measurements of the different channels andthe correlation between the interference levels of different channels isadditionally used, when allocating the listening channels of the BBNs.

FIG. 10, Allocation Method with Bias to More Recent ReceptionPerformance

FIG. 10 shows another embodiment with allocation biased towards morerecent reception performance. The steps are as shown in FIG. 9, but inplace of step 210 there is a step 214 of updating a database ofreception performance information for different BBNs and channels at asequence of times. In place of step 220, there is a step 224 in which anoutage probability matrix for various possible allocation patterns fordifferent BBNs and different radio channels can be derived at step 224from the reception performance database, with a bias to be moredependent on more recent reception performance detections. This can beimplemented following some of the details set out in the exampledescribed above, adapted to introduce the bias, so that the informationderived from packet a_(i+j) is assigned a higher weight than theinformation from a_(i+j−1) when estimating the packet error rates forfuture packets.

FIG. 11, Allocation Method for Multiple ULP Nodes

FIG. 11 shows another embodiment showing reception performance detectionand allocation coordinated for multiple ULPNs The steps are as shown inFIG. 9, but in place of step 200 there is a step 202 of collectingindications of reception performance such as RSSIs from different BBNsfor multiple ULPNs. In place of step 210, there is a step 212 ofupdating a database of reception performance information for theindications of reception performance relating to the multiple ULPNs. Inplace of step 220, there is a step 222 of deriving an outage probabilitymatrix for the multiple ULPNs. Again this can be implemented followingsome of the details of the example described above. In other words:

ULP Node A broadcasts its packets on at least two radio channels, andULP Node B broadcasts its packets on at least two radio channels. Apacket a_(i) broadcasted by ULP Node A, is received by a subset of theBackbone Nodes, and a packet β_(i) broadcasted by ULP Node B is receivedby the same or a different subset of the Backbone Nodes. For each of theBackbone Nodes and for each of the radio channels ULP Node A, (orrespectively ULP Node B), is capable of transmitting on, dynamically(regularly or triggered by the reception by the backbone network of apacket transmitted by one of the ULPNs), an estimate is made of thepacket error rates for a future packet a_(i+n), (or respectivelyβ_(i+n)), with n>0, based on the reception performance information. Thisinformation can include whether the packet a_(i), (or respectivelypacket β_(i)), was or was not received by the respective BBNs, and thechannel, signal strength and link quality associated with the eventualreception for example.

Combining the estimated packet error rates on a network scale level, todynamically allocate the listening channels of the BBNs, enablesprocessing in order to maximize the probability that a future packeta_(i+n) or a future packet β_(i+n) is received by at least one of theBBNs, in case of interference on one or more of the radio channels ULPNode A is broadcasting.

FIG. 12 Allocation Method with Location Information

FIG. 12 shows another embodiment showing allocation based on locationsof BBNs and/or ULPNs. The steps are as shown in FIG. 9, but in place ofstep 220 the step of deriving outage probability 226 is based also oncorrelations from information about locations of detections for example.Various examples using the location of the ULPNs and/or of the BBNs as afactor can be envisaged. For example the relative location of the ULPNsand BBNs can be used to build an interference level map. This can beused additionally as a factor when estimating the packet error rate forfuture packets on the different channels. The location information canbe derived from RSSI, LQI or transmission delay (chirp based)measurements, or can be a priori knowledge of the system for example.

Variety of Interference Conditions Various types of interference arepossible. The assumed type of interference can affect the best approachto follow with regard to the selection of BBN channel frequencies. Theinterference might differ in properties as follows:Local Versus Global Interference.

In the case of global interference there will be a strong correlationbetween the interference level seen by the different BBNs, for a givenchannel and a given time. Knowledge of this correlation can be exploitedto optimize the channel allocations.

Small Band Interferer Versus Wideband Interferer.

In case of a wideband interferer, there will be a strong correlationbetween the interference levels seen on different channels by a givenBBN for a given time. Knowledge of this correlation can be exploited tooptimize the channel allocations.

Continuous Versus Burst Interference.

In case of a burst interferer the interference is not always present,but comes and goes in time. Certain patterns might be recognized, suchas dependency on time of day, which could be exploited to optimize thechannel allocations.

The Level of Interference the Interferer Generates

A low level interferer degrades the ability of the BBNs to receive thepackets from the ULPNs, while a high level interferer completely blocksthe ability of the BBNs to receive the packets from the ULPNs.

The invention claimed is:
 1. A method of operating a wireless interfacefor communicating between an ultra low power wireless node and a networkof backbone nodes, the method having the steps of: making transmissionsfrom the ultra low power wireless node to send a same packet on at leasttwo radio channels, receiving the transmissions carrying the same packetat the backbone nodes on radio channels used by the ultra low powerwireless node for transmitting, detecting reception performance of thewireless interface, wherein reception performance includes both receivedsignal strength indicators (RSSIs) and timing information ofinterference associated with packet transmissions of the same packetreceived on the at least two radio channels by the backbone nodes andcorrelation of the timing information of the interference detected andRSSI level of the interference measured for the same packet overmultiple backbone nodes, assigning a higher weight to an indication ofthe reception performance that comprises the RSSI and timing informationof interference that is the timing of when the interference was detectedat each backbone node at a first time than to an indication of thereception performance detected at a previous time, and dynamicallyallocating which of the radio channels are listened for at the backbonenodes according to a greater bias towards the higher weighted indicationof the detected reception performance, wherein the dynamicallyallocating comprises making coordinated allocations for different onesof the backbone nodes.
 2. The method of claim 1, the step of making thetransmissions from the ultra low powered wireless node being madewithout dynamic radio channel selection based on radio channel selectionfeedback information from the backbone nodes.
 3. A method of allocatinglistening radio channels for a wireless interface for communicatingbetween an ultra low power wireless node and a network of backbonenodes, for use when the ultra low power wireless nodes sendtransmissions having a same packet on at least two radio channels, forreceiving the transmission carrying the same packet at the backbonenodes on radio channels used by the ultra low power wireless node fortransmitting, the method having the steps of: receiving an indication ofreception performance of the wireless interface, wherein receptionperformance includes both received signal strength indicators (RSSIs)and timing information of interference associated with packettransmissions of the same packet received on the at least two radiochannels by the backbone nodes and correlation of the timing informationof the interference and RSSI level of the interference measured for thesame packet over the at least two radio channels, assigning a higherweight to an indication of the reception performance that comprises theRSSI and timing information of interference that is the timing of whenthe interference was detected at each backbone node at a first time thanto an indication of the reception performance detected at a previoustime, and allocating dynamically which of the radio channels arelistened for at the backbone nodes according to a greater bias towardsthe higher weighted indication of the detected reception performance,wherein the dynamically allocating comprises making coordinatedallocations for different ones of the backbone nodes.
 4. The method ofclaim 3, the indication of the reception performance of thetransmissions comprising an indication of whether the packet wasreceived by the backbone nodes and further comprising at least one of:carrier sense assessments of interference measured, correlation ofinterference over multiple backbone nodes, and interference detected atthe ultra low power wireless node and sent to the backbone nodes.
 5. Themethod of claim 3, wherein the step of allocating comprises passing thedetections of reception performance by at least two of the backbonenodes to a common location and making the allocations based on thedetections collected at that common location.
 6. The method of claim 3,the step of dynamically allocating comprising the step of determiningoutage probabilities for each radio channel for each of the backbonenodes for different patterns of listening channel allocations accordingto the detections and carrying out the allocating based on thedetermined outage probabilities.
 7. The method of claim 3, wherein thetransmissions comprise transmissions from at least two ultra low powerwireless nodes, and the detecting step comprises detecting receptionperformance of the transmissions from the at least two ultra low powerwireless nodes and wherein the allocating step comprises makingallocations for listening channels of the backbone nodes from the set oftransmit channels used by the at least two ultra low power wirelessnodes.
 8. The method of claim 7, and having the step of determiningoutage probabilities for each of the ultra low power wireless nodes foreach of the backbone nodes for each of the radio channels for each ofthe channel allocation patterns.
 9. The method of claim 3, wherein thestep of making the allocations is also dependent on locations of theultra low power wireless node and of the backbone nodes.
 10. A computerprogram stored on a non-transitory computer-readable medium forallocating listening radio channels for a wireless interface forcommunicating between an ultra low power wireless node and backbonenodes, for use when the ultra low power wireless nodes sendtransmissions having the same packet on at least two radio channels, forreceiving at the backbone nodes, the program having instructionsexecuted by a processor to carry out the method of claim
 3. 11. Anapparatus for allocating listening radio channels of a wirelessinterface for communicating between an ultra low power wireless node anda network of backbone nodes, for use when the ultra low power wirelessnodes are arranged to send transmissions having a same packet on atleast two radio channels, for receiving at the backbone nodes thetransmissions carrying the same packet on radio channels used by theultra low power wireless node for transmitting, the apparatus having aninput for receiving an indication of reception performance of thewireless interface between the ultra low power wireless node and thebackbone nodes, wherein reception performance includes both receivedsignal strength indicators (RSSIs) and timing information ofinterference associated with packet transmissions of the same packetreceived on the at least two radio channels by the backbone nodes andcorrelation of the timing information of the interference and RSSI levelof the interference measured for the same packet over the at least tworadio channels, and a processor configured to: assign a higher weight toan indication of the reception performance that comprises the RSSI andtiming information of interference that is the timing of when theinterference was detected at each backbone node at a first time than toan indication of the reception performance detected at a previous time,and allocate dynamically which of the radio channels are listened for atthe backbone nodes according to a greater bias towards the higherweighted indication of the detections of reception performance, whereinthe allocating comprises making coordinated allocations for differentones of the backbone nodes, and outputting the allocations to thebackbone nodes.
 12. The apparatus of claim 11, the processor also beingconfigured to determine outage probabilities for each radio channel foreach of the backbone nodes for different patterns of listening channelallocations according to the indications and to carry out the allocatingbased on the determined outage probabilities.
 13. A network having theapparatus of claim 11, and having backbone nodes coupled to theapparatus, the backbone nodes being configured to detect the receptionperformance and to send the indications of the reception performance tothe apparatus.